1. Field of the Invention
The present invention provides the pixel structure of a liquid crystal display (LCD) and a forming method thereof. In particular, the pixel structure has multiple distinct alignment films and the forming method thereof.
2. Descriptions of the Related Art
Currently in common liquid crystal displays (LCDs), the alignment orientations of the liquid crystal molecules are altered by applying voltages externally to acquire varied optical characteristics. For example, a twisted nematic (TN) type LCD basically comprises an upper and a lower conductive glass substrates, a nematic liquid crystal layer injected between the substrates, two polarizers disposed on the outer surfaces of the two substrates respectively, and alignment films coated on the conductive glass substrates with very fine trenches formed therein by rubbing. The fluidity of the liquid crystal molecules tends to align the molecules along the trench direction. The trenches in the alignment films of the upper and the lower conductive glass substrates differ from each other by 90°. Consequently, when filled into the trenches of the upper and the lower substrates, the liquid crystal molecules will be aligned along the trench directions, with the liquid crystal molecules in the middle subjected to the smaller binding force. Those molecules closer to the trenches of the substrates are subjected to a larger binding force. In general, the liquid crystal molecules will be aligned at a twisted angle of 90°.
When there is no voltage applied, the light entering the liquid crystal element propagates with the polarization that changes according to the twisted direction of the liquid crystal molecules. Because the upper and lower polarizers have the same directions as the upper and lower alignment films respectively, the light is transmitted through the liquid crystal elements to provide brightness. In contrast, when a voltage is applied, the liquid crystal molecules are aligned towards a direction in which the electric field is applied and are consequently aligned perpendicularly to the alignment films. In this case, the light will not be able to transmit through the second polarizer, thus yielding darkness. Such alternate bright and dark statuses may be used for display purposes.
As another example, in a vertical alignment (VA) LCD, protrusions are used to cause the liquid crystal molecules to present a pre-tilt angle in a stationary alignment status, so that when applied with a voltage, the liquid crystal molecules will tilt towards various orientations rapidly. The light from the back light source can be transmitted through rapidly after applying the voltage to shorten the display response time remarkably. Furthermore, because the protrusions lead to a change in the orientation of the liquid crystal molecules, the liquid crystal molecules may reinforce each other when the LCD is viewed from different angles, thus obtaining an enlarged viewing angle range.
In current thin-film transistor liquid crystal displays (LCD-TFTs), the glass substrates are coated with an alignment material to provide a certain alignment effect. However, since the rubbing alignment method may provide alignment in only one single direction, gray-scale inversion tends to occur at particular viewing angles. Moreover, in VA type LCDs, the color is washed out at large viewing angles, resulting in a significantly degraded chroma viewed by a viewer at large viewing angles.
In an attempt to solve the aforementioned problems, some patents have proposed to pattern the alignment films by a development and etching process or to modify the alignment films with plasma. However, all of these methods require additional photo-resist coatings, exposures, development and etching, which not only increases the complexity of the manufacturing process, but also leads to lengthened processing time and increasing costs. In summary, it is highly desirable in the art to overcome the problems associated with the alignment of different alignment films by a simple manufacturing process.